CHICAGO -- Environmental pollution may be contributing to the growing incidence of liver disease in the general U.S. population, researchers found.

Action Points

Explain to interested patients that this study found that exposure to pollutants, even some banned decades ago, may cause liver disease.

Point out that this was a cross-sectional study, and as such, could not prove a causal relationship between pollution and liver disease.

Note that this study has been published as an abstract and will be presented orally at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

CHICAGO, May 29 -- Environmental pollution may be contributing to the growing incidence of liver disease in the general U.S. population, researchers found.

More than one-third of U.S. adults (37.6%) had elevated alanine aminotransferase (ALT) levels, even after those with risk factors such as hepatitis B or C infection, a history of alcohol abuse, or iron overload were excluded, according to Matthew Cave, M.D., of the University of Louisville in Kentucky.

Cross-sectional analyses found that at least some of this burden may be attributed to exposure to environmental pollutants, including banned organochloride pesticides and heavy metals such as mercury and lead.

"These results indicate that there may be a previously unexpected role for environmental pollution in the rising incidence of liver disease in the U.S. population," Dr. Cave said.

"This is the first study to my knowledge, epidemiologic study anyway, that shows that this is a problem," he added.

He will present the findings on Sunday at Digestive Disease Week here.

On the basis of the results, Dr. Cave estimated that 70 million U.S. adults have liver disease not explained by traditional risk factors, which can be mostly attributed to nonalcoholic fatty liver disease.

Previous work by Dr. Cave's group has established a link between high occupational exposures to chemicals and liver disease, but it had remained unknown whether chronic, low-level exposure to pollutants was associated with liver abnormalities in the general population.

So, using data from the National Health and Nutrition Examination Survey (NHANES) for 2003-2004, the researchers identified adults with detectable levels of 196 different pollutants in their blood or urine.

Only the 111 toxicants present in 60% or more of the participants were included in the analysis.

After excluding participants with known risk factors for liver disease, researchers found that nearly 40% had elevated ALT levels (greater than 30 U/L for men and 19 U/L for women).

At the class level, increasing levels of heavy metals (P=0.015) and pesticides (P<0.001) were both associated with higher odds of having elevated ALT levels after adjusting for age, sex, race, poverty, insulin resistance, and body mass index.

Participants who had the highest levels of mercury had double the risk of an elevated ALT, the surrogate for liver disease (OR 2.2, P<0.001), and those who had the highest levels of lead had triple the risk (OR 3.3, P=0.026).

Higher levels of two organochlorine pesticides banned in the U.S. for almost all purposes since the 1970s and 1980s, dieldrin (P=0.027) and heptachlor epoxide (P=0.009), were also significantly associated with an increased risk of liver disease.

"They were bad then and they're still bad today," Dr. Cave said. "One of the things that was remarkable to me was that the detection rates of these things were extremely high, so they're clearly persistent organic pollutants."

The major route of exposure for many of the pollutants included in the study is through the food supply, he said, and once they are in the body, they are not well metabolized.

Organochloride pesticides in particular accumulate in adipose tissue, so that individuals who are more overweight have higher levels, Dr. Cave said.

He pointed out, however, that a cross-sectional analysis cannot prove causality. One could argue, he said, that patients with liver disease are less capable of metabolizing these pollutants, and that explains the higher levels.

But animal studies have shown that these pesticides and other pollutants cause liver disease, he said.

"So I believe that it's very plausible that these caused the liver disease" in this study, he said.

Funding for the study was provided by an American Association for the Study of Liver Diseases (AASLD) Sheila Sherlock Award to Dr. Cave and by the National Institute of Environmental Health Sciences.